Patent GB-1159359-A (GB)
Title: Improvements in or relating to Vehicle Hydraulic Brake Systems
IPC: B60T13/52
Filed: 1967-12-05
Abstract: 1,159,359. Vehicle braking systems; link-work; valves. KELSEY-HAYES CO. 5 Dec., 1967 [12 Dec., 1966], No. 55243/67. Headings F2E, F2F, F2K and F2V. An assisted dual master-cylinder braking system comprises a brake pedal acting on a linkage system which is attached at three separate points to the two master cylinders and to a device producing a force dependent on relative movement of different parts of the linkage system or on movement of the brake pedal. In Fig. 1, the brake pedal 69 has a lug 72 to which is pivoted at 74 a link 73, this in turn being pivoted at 77 about a larger link 76. Depression of the pedal causes link 73 to rotate counterclockwise about 77 and pull to the right a tube 50 which is attached at 79 to the lower end of link 73. The other end of this tube is attached via a cylindrical portion 49 to a plate 42 which forms one of the clamping rings of a diaphragm 37. A chamber 66 on the other side of the diaphragm is normally in communication with the atmosphere through apertures 48 in the diaphragm and passages 56, 57, 54, but on movement of the tube 50, the diaphragm seats against the open end of passage 56 and blocks the connection. At the same time, an annular groove 61 in the end of the member 49 moves away from the diaphragm and connects the chamber 66 through passages 62, 64 to a source of vacuum (not shown). The diaphragm is now sucked to the left and pulls the tube 50, so that a pin 75 on the end rotates the link 76. The end 82 of this link urges a rod 30 to operate the piston 18 of a master cylinder 12 connected to the rear brakes. The movement of the diaphragm continues until the force applied to the link 76 via tube 50 and pin 75 equals that from the brake pedal applied via pin 74. Then the link 76 moves linearly to the left and both master cylinders 11, 12 will be operated equally, the former supplying the front brakes. The diaphragm and tube 50 contribute servo assistance. On further depression of the brake pedal, a point is reached when the vacuum source is no longer able to apply a force equal to that of the brake pedal. The link 76 then allows a spring-loaded rod 52 inside the tube 50 to move to the right, opening the end of the passage 56 and connecting the chamber 66 to the atmosphere. The servo assistance now ceases, the pin 74 abuts the left-hand side of the hole 78 and the brake pedal alone moves the master-cylinder pistons. Since the point 74 where the pedal force is applied is nearer to cylinder 11 than to cylinder 12, the former will experience a greater pressure, and the front wheels will be braked harder than the rear wheels. The point at which the change-over takes place depends on the lever ratios of the links 73, 76 and on the strength of the vacuum. The latter is controlled by a valve (Fig. 2) in the line between the vacuum source (connected at 92) and the tube 64 (connected at 93). A valve stem 94 is held open by a spring 98 abutting a piston 95 until the vacuum reaches a certain level, when the valve closes under the influence of a spring 91. This can be controlled by a knob 89 or be connected to an unsprung portion of the vehicle to provide automatic control according to the load on the vehicle. The relative braking force on the front and rear wheels can thus be controlled in accordance with deceleration which produces a shift in the relative loading of the front and rear axles.